Today's Astronomy Picture of the Day is one of my favorite images -- a composite view of the Crab Nebula, created by combining images from the Hubble Space Telescope and the Chandra X-Ray Observatory.

The real nebula wouldn't look precisely like this, unless you have X-ray vision. (When I was growing up, pictures of the Crab Nebula looked like this. And we thought it was cool when they started to look like this. Kids today are so spoiled.) The blue part of the image comes from the X-rays observed by Chandra, while the red part is the optical light measured by HST; you can easily make out a disk, several light-years across, as well as a jet being emitted perpendicular to the disk. The energy driving the emission comes from a pulsar at the center of the disk. The pulsar is a rapidly rotating neutron star, the remnant of a supernova explosion observed here on Earth in 1054. Interestingly, the event was recorded by astronomers in China and also by Native Americans, but not by any European or Arab astronomers.

Don't miss the movies of ripples propagating through the jet and disk.